Tool-holding system for high-accuracy calibration of holes

ABSTRACT

The invention relates to the field of toolings for high-accuracy finishing through-holes and non-through-holes, such as for example for calibration, lapping operations. More precisely the invention refers to a tool-holding system for high-accuracy calibration of the type comprising a driving shaft ( 2 ) and a driven shaft ( 3 ) mutually connected by two cardan joints ( 5 ) and that provides an external cylindrical body ( 6 ) supported through bearings ( 8 ) by said driving shaft ( 2 ). The cylindrical body or liner ( 6 ) is closed on its bottom side by a driving bush oscillating in a plane perpendicular to the driven shaft rotation axis; said oscillations being compensated by elastic means. Axial compensation means for driven shaft movements are also provided. The liner ( 6 ) forms a chamber ( 7 ) that is kept full of oil.

Object of the present invention is a tool-holding system forhigh-accuracy calibrating through-holes and non-through-holes.

This system, as for example a spindle does, must perform the function ofrotating a high-accuracy calibrating tool placed on a driven shaft in amisaligned position with respect to a driving shaft of the system itself

Due to the above-mentioned misalignment of the driving shaft withrespect to the drive shaft, two cardan joints must be inserted betweensaid shafts.

As known, the insertion of cardan joints generates on the driven shafttransverse oscillating forces that are unacceptable for the type ofworking.

In fact, the present invention refers to those types of systems withvarious connections adapted to carry tools used for workings such ascalibration and lapping or vertical holes, that imply reaching amicrometric accuracy degree on the order of a dimensional tolerancewidth equal to or included between IT1 and IT5 according to ISO systemand geometric tolerances on the order of 2 μm of cylindricity and 1 μmof roundness and a surface roughness less than 0.2 Ra (approximate).

The above workings refer to processes for removing ferrous materials andnot through abrasion.

In the following description the term “spindle” will be used forgenerically referring to any tool-holding system.

Through vertical-axis spindles with cardan joints currently known on themarket, the required accuracy degree is not able to be reached due tovibrations induced both by working and by the cardan junction betweenthe two shafts.

Moreover, resonance phenomena occur, that are triggered due to externalforces, such as, for example, vibrations to which the spindle issubjected due to the driving motor; these are forced vibrations due toperiodic thrusts.

Another great disturbance phenomenon is due to the precession motion,namely to the motion of a cylindrical body rotating around its owngeneratrix that continuously change its angle, with respect to avertical line, due to the angular moment operating on the body (atypical example of precession motion being the one of a topwhose-rotation axis is initially slanted with respect to the vertical).

In order to reduce the oscillation amplitude, an external cylindricalbody or liner has been inserted, constrained through ball bearings tothe driving shaft.

The cylindrical body is locked in its rotation by an external constraintsecured to the fixed structure of the spindle-holding machine, while itsvertical axial dragging is allowed with the driving shaft.

By inserting the external cylindrical body or liner, the oscillationamplitude has been reduced, but not in such a way as to comply with theabove-required tolerances.

Object of the present invention is removing the above-mentionedinconveniences by providing a tool-holding system that is able to reachthe above-required finishing degrees and in particular to reach radialmovement values of the driven shaft equal to ±1–1.5 mm and axialmovement values equal to ±10–15 degrees.

Only with the above-mentioned movement values a high-accuracycalibration with blocked workpiece can be reached.

These and other objects are fully reached by the tool-holding system forhigh-accuracy calibration of the present invention, that ischaracterised by the contents of the below-mentioned claims and inparticular in that it comprises, in combination, a cylindrical body orliner wrapped around the joints and creating a chamber in whichlubrication and cooling oil is kept, this chamber being closed on itsbottom side by a driving bush oscillating in a plane perpendicular tothe tool rotation axis. Compensation means for radial and axialoscillations of the tool-holding driven shaft are provided.

This and other features will be better pointed out by the followingdescription of two preferred embodiments shown, as a purely non-limitingexample, in the enclosed drawings, in which:

FIG. 1 shows the tool-holding system in a longitudinal section andaccording to a first embodiment;

FIG. 2 shows part of the driven shaft with the diagram of oscillationswhose amplitude is contained within said driven shaft diameter;

FIG. 3 shows the tool-holding system in a longitudinal section andaccording to a second embodiment.

With reference to FIG. 1, reference 1 globally refers to a spindle bodyas a whole that provides for a driving shaft 2 and a driven shaft 3 onwhich, according to known techniques, a tool 4 is assembled that iscomposed, as an example, of an abrasive bush with different grain grades(for example a diamond bush or a boron nitride bush).

Generally the driven shaft can rotate along both directions. The drivingshaft is connected to the driven shaft through two cardan joints 5.

Reference 6 shows another external cylindrical body or liner that iswrapped around the whole area occupied by the two cardan joints creatingan annular chamber 7.

The cylindrical body 6 is connected and supported by the driving shaftthrough two bearings 8 and its rotation is prevented through a pipe 9that is engaged into an hole 10 that communicates with the annularchamber 7.

Pipe 9, that is used to continuously supply lubrication and cooling oilto chamber 7, is kept secured to the machine structure, not shown,through a lock rod 16.

Cylindrical body 6 is closed on its bottom side by a driving slidingbush 11 that is housed in a cylindrical body recess 13.

The driven shaft driving bush is compensated by a plurality of springs12 that exert radial elastic thrusts onto said bush.

More precisely the driving bush 11 is free of moving on the orthogonalplane to the tool rotation axis, but is kept in position, in theabove-described embodiment, by four springs 12 which can be calibratedaccording to needs.

All cardan joints and driven shaft assembly can then radially float andoscillations are compensated by radial compensating means composed ofthe four springs.

Axial compensating means are also provided vertically and are composedof a further helical spring 14 placed over the upper cardan joint.

Function of oil in chamber 7, in addition of operating for lubrifyingand cooling all moving members, is hydraulically dampening theoscillating movements.

As can be noted from FIG. 2, with the above-described tool-holdingsystem, it has been possible to greatly reduce the oscillationamplitudes, shown by curve 15, that are, contained within the drivenshaft diameter.

With reference to FIG. 3, in case an expansion tool 17 is assembled ondriven shaft 3, a supplementary double cardan joint 18 is also provided,as an articulation instrument, placed along the central spindle body andcoaxial with driven shaft 3 that carries the tool, in order to guaranteethe correct oscillation dampening.

This solution, technically equivalent to the previous one, provides fora stabilising cylindrical body 19 that carries the four springs 12exerting radial thrusts. The stabilising cylindrical body, kept fixed,is supported by a rotating cylindrical body or liner 21 through the twobearings 20.

Obviously numerous modifications and variations could be provided, allfalling within the scope of the claims below, such as for example thenumber of springs can be different from the described one, as well aselastic thrusts can also be exerted by other means such as small blocksmade of rubber or other synthetic elastic material or compressed-aircylinders, etc.

The type of used springs could be different, such as for exampleBelleville washers or other types of springs.

With the above-described tool-holding system, numerous advantages areobtained, in addition to the one of reaching a finishing and accuracydegree that was not able to be reached previously with cardan jointspindles, such as for example:

-   -   it is possible to make blind holes too;    -   reduction of tooling times and costs;    -   correct balancing neutralization for moving masses to be worked;    -   reduced length encumbrances with respect to the vertical working        axis.

1. An improved tool-holding system including a driving shaft connectedthrough first and second cardan joints to a driven shaft carrying atool, the improvement comprising: an external cylindrical bodysurrounding the cardan joints and creating a chamber between the cardanjoints and the body, the chamber being closed on a bottom side by adriving bush of the driven shaft, the driving bush being substantiallyadjacent an end of the driven shaft connected to the second cardan jointand oscillating in a plane perpendicular to a rotation axis of saiddriven shaft, said chamber being supplied by lubricating and coolingoil; elastic means for compensating radial oscillations of the drivenshaft adapted to keep the driving bush in position; axial compensatingmeans adapted to compensate vertical movements of the driven shaft. 2.Tool-holding system according to claim 1 further comprising at least onebearing keyed onto the driving shaft and supporting the cylindricalbody, the cylindrical body being retained against rotation while thedriving shaft rotates.
 3. Tool-holding system according to claim 1characterised in that the radial compensating elastic means comprises aplurality of springs uniformly radially arranged about the cylindricalbody thickness and engaging the driving bush.
 4. Tool-holding systemaccording to claim 1 characterised in that the axial compensating meanscomprises a spring placed between driven shaft and driving shaft. 5.Tool-holding system according to claim 1 characterised in that bothaxial compensating means and radial compensating means are adjustable toallow the compensating means to be calibrated.
 6. Tool-holding systemaccording to claim 1 further comprising an oil supply pipe into thechamber that is also a rotation-locking member for the cylindrical body.7. Tool-holding system according to claim 1 characterised in that theradial compensating means, the axial compensating means, and oil inchamber cooperate to limit an amplitude of an oscillation of the drivenshaft within the driven shaft diameter.
 8. A tool-holding systemcomprising: a drive shaft connected to a driven shaft via first andsecond cardan joints, the driven shaft being axially movable relative tothe drive shaft and supporting and driving a tool; a substantiallycylindrical body substantially coaxial with axes of rotation of thedrive shaft, driven shaft, and the first and second cardan joints; thesubstantially cylindrical body surrounding the cardan joints and beingheld against rotation; an annular chamber surrounding the cardan jointsbetween the cardan joints and the substantially cylindrical body; a bushat a lower end of the substantially cylindrical body covering the lowerend adjacent a juncture of the second cardan joint and the driven shaftand movable in a plane transverse to a longitudinal axis of thesubstantially cylindrical body; at least one bush elastic member, afirst end of each of the at least one bush elastic member engaging thebush and a second end of each of the at least one bush elastic memberengaging the substantially cylindrical body, thereby retaining the bushsubstantially coaxial with the substantially cylindrical body whileallowing some movement in the plane and damping vibration in the plane;and at least one axial elastic member between the drive shaft and drivenshaft and arranged to dampen axial movement of the drive shaft.
 9. Thetool-holding system of claim 8 wherein the at least one bush elasticmember comprises a plurality of radially-arranged coil springs.
 10. Thetool-holding system of claim 8 wherein the at least one axial elasticmember comprises a spring in an end of the drive shaft closest to thedriven shaft.
 11. The tool-holding system of claim 10 wherein a firstend of the spring engages the end of the drive shaft and a second end ofthe spring engages one of the cardan joints.
 12. The tool-holding systemof claim 8 further comprising an oil supply hole through which oil canenter the annular chamber, the oil lubricating, cooling, and dampeningvibration of the elements within the substantially cylindrical body. 13.The tool-holding system of claim 12 further comprising a locking rodinsertable into the oil supply hole that retains the substantiallycylindrical body against rotation.